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NURS1004 Week 13 Lecture
Control of Respiration Part III
prepared by Didy Button
23-10 Control of Respiration
• Peripheral and Alveolar Capillaries
– Maintain balance during gas diffusion by:
1. Changes in blood flow and oxygen delivery
2. Changes in depth and rate of respiration
23-10 Control of Respiration
• Local Regulation of Gas Transport and Alveolar Function
• Rising PCO levels
2
– Relax smooth muscle in arterioles and capillaries
– Increase blood flow
• Coordination of lung perfusion and alveolar ventilation
– Shifting blood flow
• PCO levels
2
– Control bronchoconstriction and bronchodilation
23-10 Control of Respiration
• The Respiratory Centers of the Brain
– When oxygen demand rises:
• Cardiac output and respiratory rates increase under
neural control
– Have both voluntary and involuntary components
23-10 Control of Respiration
• The Respiratory Centers of the Brain
– Voluntary centers in cerebral cortex affect:
• Respiratory centers of pons and medulla oblongata
• Motor neurons that control respiratory muscles
– The Respiratory Centers
• Three pairs of nuclei in the reticular formation of
medulla oblongata and pons
• Regulate respiratory muscles
• In response to sensory information via respiratory
reflexes
Figure 14-12b The Brain in Lateral View
Precentral
gyrus
Central
sulcus
Postcentral
gyrus
PARIETAL LOBE
FRONTAL
LOBE
OCCIPITAL
LOBE
TEMPORAL
LOBE
Lateral sulcus
Cerebellum
Pons
Medulla oblongata
Lateral view
23-10 Control of Respiration
• Respiratory Centers of the Medulla Oblongata
– Set the pace of respiration
– Can be divided into two groups
1. Dorsal respiratory group (DRG)
2. Ventral respiratory group (VRG)
23-10 Control of Respiration
• Dorsal Respiratory Group (DRG)
– Inspiratory center
– Functions in quiet and forced breathing
• Ventral Respiratory Group (VRG)
– Inspiratory and expiratory center
– Functions only in forced breathing
23-10 Control of Respiration
• Quiet Breathing
– Brief activity in the DRG
• Stimulates inspiratory muscles
– DRG neurons become inactive
• Allowing passive exhalation
Figure 23-25a Basic Regulatory Patterns of Respiration
Quiet Breathing
INHALATION
(2 seconds)
Diaphragm and external
intercostal muscles
contract and inhalation
occurs.
Dorsal
respiratory
group
inhibited
Dorsal
respiratory
group active
Diaphragm and
external intercostal
muscles relax and
passive exhalation
occurs.
EXHALATION
(3 seconds)
23-10 Control of Respiration
• Forced Breathing
– Increased activity in DRG
• Stimulates VRG
• Which activates accessory inspiratory muscles
– After inhalation
• Expiratory center neurons stimulate active exhalation
Figure 23-25b Basic Regulatory Patterns of Respiration
Forced Breathing
INHALATION
Muscles of inhalation
contract, and opposing
muscles relax
Inhalation occurs,
DRG and
inspiratory
center of VRG
are inhibited.
Expiratory
center of VRG
is active.
DRG and
inspiratory
center of VRG
are active.
Expiratory center
of VRG is
inhibited.
Muscles of inhalation
relax and muscles of
exhalation contract.
Exhalation occurs.
EXHALATION
23-10 Control of Respiration
• Respiratory Centers and Reflex Controls
– Interactions between VRG and DRG
• Establish basic pace and depth of respiration
– The pneumotaxic center
• Modifies the pace
Figure 23-26 Control of Respiration
Respiratory Centers and Reflex Controls
The locations and
relationships
between the major
respiratory centers in
the pons and medulla
oblongata and other
factors important to
the reflex control of
respiration. Pathways
for conscious control
over respiratory
muscles are not
shown.
Cerebrum
HIGHER CENTERS
Cerebral cortex
Limbic system
Hypothalamus
Pons
CSF
CHEMORECEPTORS
Pneumotaxic
center
KEY
Apneustic
center
= Stimulation
= Inhibition
Medulla
oblongata
Figure 23-26 Control of Respiration
Respiratory Centers and Reflex Controls
Medulla
oblongata
N IX and N X
Chemoreceptors and
baroreceptors of carotid
and aortic sinuses
Diaphragm
NX
Stretch
receptors
of lungs
Spinal
cord
Respiratory Rhythmicity
Centers
Dorsal respiratory
group (DRG)
Ventral respiratory
group (VRG)
Motor neurons
controlling
diaphragm
Motor neurons
controlling other
respiratory muscles
KEY
Phrenic nerve
= Stimulation
= Inhibition
23-10 Control of Respiration
• Respiratory Reflexes
– Chemoreceptors are sensitive to PCO2, PO2, or pH of
blood or cerebrospinal fluid
– Baroreceptors in aortic or carotid sinuses are
sensitive to changes in blood pressure
– Stretch receptors respond to changes in lung volume
– Irritating physical or chemical stimuli in nasal cavity,
larynx, or bronchial tree
– Other sensations including pain, changes in body
temperature, abnormal visceral sensations
23-10 Control of Respiration
• The Chemoreceptor Reflexes
– Respiratory centers are strongly influenced by
chemoreceptor input from:
• Glossopharyngeal nerve (N IX) (9th Cranial Nerve)
• Vagus nerve (N X) (10th Cranial Nerve)
• Central chemoreceptors that monitor cerebrospinal fluid
23-10 Control of Respiration
• The Chemoreceptor Reflexes
– The glossopharyngeal nerve
• From carotid bodies in the carotid artery
• Stimulated by changes in blood pH or PO
2
– The vagus nerve
• From aortic bodies in the aorta
• Stimulated by changes in blood pH or PO
2
23-10 Control of Respiration
• The Chemoreceptor Reflexes
– Central chemoreceptors that monitor
cerebrospinal fluid
• Are on ventrolateral surface of medulla oblongata
• Respond to PCO and pH of CSF
2
23-10 Control of Respiration
• Chemoreceptor Stimulation
– Leads to increased depth and rate of
respiration
– Is subject to adaptation
• Decreased sensitivity due to chronic stimulation
23-10 Control of Respiration
• Hypercapnia
– An increase in arterial PCO
2
– Stimulates chemoreceptors in the medulla
oblongata
• To restore homeostasis
23-10 Control of Respiration
• Hypercapnia and Hypocapnia
– Hypoventilation is a common cause of hypercapnia
– Abnormally low respiration rate
• Allows CO2 buildup in blood
– Excessive ventilation, hyperventilation, results in
abnormally low PCO (hypocapnia)
2
• Stimulates chemoreceptors to decrease respiratory rate
Figure 23-27a The Chemoreceptor Response to Changes in PCO2
Increased
arterial PCO2
Stimulation
of arterial
chemoreceptors
Stimulation of
respiratory muscles
Increased PCO2 ,
decreased pH
in CSF
Stimulation of CSF
chemoreceptors at
medulla oblongata
Increased respiratory
rate with increased
elimination of CO2 at
alveoli
HOMEOSTASIS
DISTURBED
Increased
arterial PCO2
(hypocapnia)
HOMEOSTASIS
Normal
arterial PCO2
Start
HOMEOSTASIS
RESTORED
Normal
arterial PCO2
Figure 23-27b The Chemoreceptor Response to Changes in PCO2
HOMEOSTASIS
Normal
arterial PCO2
Start
HOMEOSTASIS
RESTORED
Normal
arterial PCO2
HOMEOSTASIS
DISTURBED
Decreased respiratory
rate with decreased
elimination of CO2 at
alveoli
Decreased
arterial PCO2
(hypocapnia)
Decreased
arterial PCO
2
Decreased PCO2 ,
increased pH
in CSF
Reduced stimulation
of CSF chemoreceptors
Inhibition of arterial
chemoreceptors
Inhibition of
respiratory muscles
23-10 Control of Respiration
• The Baroreceptor Reflexes
– Carotid and aortic baroreceptor stimulation
• Affects blood pressure and respiratory centers
– When blood pressure falls:
• Respiration increases
– When blood pressure increases:
• Respiration decreases
23-10 Control of Respiration
• Protective Reflexes
– Triggered by receptors in epithelium of respiratory
tract when lungs are exposed to:
• Toxic vapors
• Chemical irritants
• Mechanical stimulation
– Cause sneezing, coughing, and laryngeal spasm
23-10 Control of Respiration
• Apnea
– A period of suspended respiration
– Normally followed by explosive exhalation to clear
airways
• Sneezing and coughing
• Laryngeal Spasm
– Temporarily closes airway
• To prevent foreign substances from entering
23-10 Control of Respiration
• Voluntary Control of Respiration
• Strong emotions can stimulate respiratory centers
in hypothalamus
• Emotional stress can activate sympathetic or
parasympathetic division of ANS
• Causing bronchodilation or bronchoconstriction
• Anticipation of strenuous exercise can increase
respiratory rate and cardiac output by sympathetic
stimulation
23-11 Effects of Aging on the Respiratory System
• Three Effects of Aging on the Respiratory System
1. Elastic tissues deteriorate
• Altering lung compliance and lowering vital capacity
2. Arthritic changes
• Restrict chest movements
• Limit respiratory minute volume
3. Emphysema
• Affects individuals over age 50
• Depending on exposure to respiratory irritants (e.g.,
cigarette smoke)
Figure 23-28 Decline in Respiratory Performance with Age and Smoking
Respiratory performance
(% of value at age 25)
Never smoked
Regular
smoker
Stopped
at age 45
Disability
Stopped
at age 65
Death
Age (years)
23-12 Respiratory System Integration
• Coordination of Respiratory and
Cardiovascular Systems
– Improves efficiency of gas exchange by controlling
lung perfusion
– Increases respiratory drive through
chemoreceptor stimulation
– Raises cardiac output and blood flow through
baroreceptor stimulation
END of Lecture Part III